Aqueous polymer emulsion and an aqueous adhesive composition formed therefrom

ABSTRACT

An aqueous polymer emulsion comprising: i) as polymerized units, from 20% to 80% by dry weight, based on total dry weight of the polymer, of vinyl acetate; ii) as polymerized units, from 20% to 80% by dry weight, based on total dry weight of the polymer, of an α, β-ethylenically unsaturated carboxylic ester monomer; iii) as polymerized units, from 0.1% to 5% by dry weight, based on total dry weight of the polymer, of a stabilizer monomer; iv) from 0.05% to 1% by dry weight, based on total dry weight of the polymer, of a surfactant, wherein said aqueous polymer emulsion has a viscosity of less than 100 cps. An aqueous adhesive composition comprising said aqueous polymer emulsion.

FIELD OF THE INVENTION

The present invention relates to an aqueous polymer emulsion. Thepresent invention also relates to an aqueous adhesive compositioncontaining such aqueous polymer emulsion which is used in laminates,textile and non-woven fabrics.

INTRODUCTION

Aqueous vinyl acetate polymer emulsions are widely used as binders inthe adhesive industry because they are relatively inexpensive comparedto acrylic emulsions. Vinyl acetate has high water solubility, a highmonomer-polymer swelling ratio, and a high chain transfer constant.However, the use of vinyl acetate monomers in adhesives may hurt theemulsion storage stability of polymer emulsions. Usually, this problemcan be solved by increasing the amount of surfactants added or by addingprotective colloids such as polyvinyl alcohol (“PVOH”) and hydroxyethylcellulose (“HEC”) to the vinyl acetate polymer emulsions to providerequired stability. However, adding high levels of surfactants is noteconomical and may have negative effect on emulsion water-sensitivity,which may cause foaming in the adhesives as well as deterioratingadhesive performance such as bond strength. The addition of protectivecolloid may also lead to high emulsion viscosity.

It is therefore desired to provide an aqueous vinyl acetate polymeremulsion with low viscosity and acceptable emulsion storage stability,and an aqueous adhesive composition containing such aqueous vinylacetate polymer emulsion with acceptable adhesive performance, such asbond strength and heat seal strength.

SUMMARY OF THE INVENTION

The present invention provides a novel aqueous vinyl acetate polymeremulsion with low viscosity and acceptable emulsion storage stability,and an aqueous adhesive composition containing such aqueous vinylacetate polymer emulsion with acceptable adhesive performance, such asbond strength and heat seal strength.

In a first aspect of the present invention there is provided an aqueouspolymer emulsion comprising: i) as polymerized units, from 20% to 80% bydry weight, based on total dry weight of the polymer, of vinyl acetate;ii) as polymerized units, from 20% to 80% by dry weight, based on totaldry weight of the polymer, of an α,β-ethylenically unsaturatedcarboxylic ester monomer; iii) as polymerized units, from 0.1% to 5% bydry weight, based on total dry weight of the polymer, of a stabilizermonomer; iv) from 0.05% to 1% by dry weight, based on total dry weightof the polymer, of a surfactant, wherein said aqueous polymer emulsionhas a viscosity of less than 100 cps.

In a second aspect of the present invention there is provided an aqueousadhesive composition comprising the aqueous polymer emulsion.

DETAILED DESCRIPTION OF THE INVENTION

An aqueous polymer emulsion comprising, as polymerized units, from 20%to 80%, preferably from 30% to 55%, and more preferably from 35% to 50%,by dry weight, based on total dry weight of the polymer, of vinylacetate.

The aqueous polymer emulsion further comprises, as polymerized units,from 20% to 80%, preferably from 45% to 70%, and more preferably from50% to 65%, by dry weight, based on total dry weight of the polymer, ofan α,β-ethylenically unsaturated carboxylic ester monomer.

Suitable examples of the α,β-ethylenically unsaturated carboxylic estermonomers include (meth)acrylic ester monomers, i.e., methacrylic esteror acrylic ester monomers such as methyl acrylate, ethyl acrylate, butylacrylate, 2-ethylhexyl acrylate, decyl acrylate, lauryl acrylate, methylmethacrylate, butyl methacrylate, isodecyl methacrylate, laurylmethacrylate, 2-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, and2-hydroxypropyl methacrylate; itaconic ester monomers such as dimethylitaconate, dibutyl itaconate; and maleic ester such as dioctyl maleate;Preferably, the α,β-ethylenically unsaturated carboxylic ester monomersare ethyl acrylate, methyl methacrylate, butyl acrylate, 2-ethylhexylacrylate, and any combinations thereof. More preferably, theα,β-ethylenically unsaturated carboxylic ester monomer are butylacrylate, 2-ethylhexyl acrylate, and any combinations thereof.

The aqueous polymer emulsion further comprises, as polymerized units,from 0.1% to 5%, preferably from 0.1% to 2.5%, and more preferably from0.1% to 1.5% by dry weight, based on total dry weight of the polymer, ofa stabilizer monomer.

Suitable examples of the stabilizer monomers include sodium styrenesulfonate, sodium vinyl sulfonate, 2-acrylamido-2-methylpropanesulfonicacid, acrylamide, acrylic acid, methacrylic acid, itaconic acid, and anycombinations thereof.

The aqueous polymer emulsion may further comprise a vinyl ester monomerother than vinyl acetate. Suitable examples of the vinyl ester monomersinclude vinyl propionate, vinyl neononanoate, vinyl neodecanoate, vinyl2-ethylhexanoate, vinyl pivalate, vinyl versatate and any combinationsthereof.

The glass transition temperature (“Tg”) of the aqueous polymer emulsionis from 8° C. to −43° C., preferably from −14° C. to −32° C., and morepreferably from −23° C. to −30° C. Tgs herein are calculated using theFox Equation (T. G. Fox, Bull. Am. Physics Soc., Volume 1, Issue 3, page123 (1956)).

The solids content of the aqueous polymer emulsion is from 30% to 60%.It is preferably from 35% to 50%, and more preferably from 41% to 45%.

The viscosity of the aqueous polymer emulsion is less than 100 cps,preferably less than 50 cps, and more preferably less than 30 cps, asmeasured by a Brookfield LVT Dial-Reading Viscometer (Spindle #2 at 60rpm).

The particle size of the aqueous polymer emulsion is from 150 nm to 500nm, and preferably from 250 nm to 350 nm.

Preferably, the aqueous polymer emulsion has a grit of less than 0.2%,preferably less than 0.02%, and more preferably less than 0.01% byweight, based on total weight of the polymer. The grit is determined byfiltering 200 g of the aqueous polymer emulsion through a 325 meshfilter, and subsequently drying and weighing the dried grit.

The polymerization process used herein can be carried out using knownmethod for preparing an aqueous emulsion polymer.

The aqueous polymer emulsion further comprises, as emulsifier, from0.05% to 1%, preferably from 0.05% to 0.5%, and more preferably from0.05% to 0.3% by dry weight, based on total dry weight of the polymer, asurfactant.

The surfactant is preferably a combination of anionic surfactant andnon-ionic surfactant with a mole ratio of the ionic surfactant to thatof the non-ionic surfactant being 0.5 to 20, preferably being 1 to 10,and more preferably being 2 to 5.

Suitable examples of the anionic surfactants include sulfates,sulfonates, phosphates, carboxylates, and any combinations thereof.Preferably, the anionic surfactant is sulfonate such as sodium dodecylbenzene sulfonate, sodium dodecyl sulfonate, sodium dodecyl diphenyloxide disulfonate, sodium n-decyl diphenyl oxide disulfonate,isopropylamine dodecylbenzenesulfonate, and sodium hexyl diphenyl oxidedisulfonate. More preferably, the anionic surfactant is sodium dodecylbenzene sulfonate.

Suitable examples of non-ionic surfactants include polyoxyethylenatedalkylphenols, polyoxyethylenated alcohols, ethylene oxide-propyleneoxide block copolymers, polyoxyethylenated fatty acid esters.Preferably, the non-ionic surfactant is polyoxyethylenated alcohols withgeneral molecule as RO—(CH₂CH₂O)_(n)H, wherein R is alkyl group. Morepreferably, alkyl group R is C₁₂-C₁₈ and oxyethylene group —(CH₂CH₂O)—is greater than 20. Commercially available non-ionic surfactant includesTERGITOL™ 15-S-40 from The Dow Chemical Company.

Preferably, protective colloid is excluded from the aqueous polymeremulsion of the present invention. Protective colloid can be (1) naturalor modified-natural products such as gum agar, gum arabic, gumtragacanth, water soluble starch, pectin, gelatin, and aliginate, andmodified cellulose such as hydroxylethyl cellulose and carboxymethylcellulose; or (2) synthetic products such as polyvinyl alcohol with ahydrolysis degree of from 70 to 100 mol %.

An aqueous adhesive composition comprising said aqueous polymer emulsionis prepared by techniques which are well known in the adhesives art.Optionally, such adhesive composition may comprise additional water,latex binder, crosslinker, and additives such as rheology modifiers,biocides, wetting and defoaming agents. Preferably, the aqueous adhesivecomposition excludes further addition of any surfactants during thepreparation of the aqueous adhesive composition.

The aqueous adhesive composition is applied onto the surface of ordinarysubstrates such as biaxially oriented polypropylene film, polyesterfilm, or nylon film, and dried to form a dry layer. The applied adhesivecomposition is considered to be dry when the remainder of water is lessthan 10% of the applied adhesive composition.

The surface of a vacuum metallized casted polypropylene film, castedpolypropylene film or polyethylene film is covered on the dry layer ofapplied adhesive composition so that a biaxially oriented polypropylenefilm/adhesive/vacuum metallized casted polypropylene film composite(composite films, and also known as the laminate) is formed. Thelaminate is preferably subjected to mechanical force to press the filmseven more closely. Such mechanical force is preferably applied bypassing the laminate between rollers. Preferably, the rollers areheated.

In the present disclosure, the technical features in each preferredtechnical solution and more preferred technical solution can be combinedwith each other to form new technical solutions unless indicatedotherwise. For briefness, the specification omits the descriptions forthese combinations. However, all the technical solutions obtained bycombining these technical features should be deemed as being literallydescribed in the present specification in an explicit manner.

Abbreviations: Acrylic acid AA Ammonia persulfate APS Butyl acrylate BABiaxially oriented polypropylene BOPP Deionized water DI waterIsoascorbic acid IAA Methacrylic acid MAA Sodium bisulfite SBS Sodiumpersulfate SPS Sodium vinyl sulfonate SVS tert-butyl hydroperoxide t-BHPVinyl acetate VA Vacuum metallized casted polypropylene VMCPP

EXAMPLES I. Raw Materials

Materials Descriptions Available from AIRVOL 205 (“PVOH A”) a partiallyhydrolyzed (87-89 Air Products mol %) PVOH CELLOSIZE ™ QP 3L a lowmolecule weight HEC The Dow Chemical (“HEC A”) Company KATHON ™ LX abiocide The Dow Chemical Company ROBOND ™ Binder L-70D a waterborneacrylic adhesive The Dow Chemical with 42% solid Company ROVACE ™ Binder662 a waterborne vinyl acrylic The Dow Chemical copolymer emulsioncomprising Company HEC as protective colloid RHODACAL ™ DS-4 an anionicsurfactant with 23% Rhodia Company surfactant (“DS-4”) solid contentTERGITOL ™ 15-S-40 a non-ionic surfactant with 70% The Dow Chemicalsurfactant (“15-S-40”) active Company VINALYST 3525 SVS with 25% activeThe Dharamsi Morarji (“V3525”) Chemical Co. Ltd.

II. Test Methods

1. Emulsion Storage Stability (Stability)

The pH value, solid content, viscosity and grit of the fresh polymeremulsion samples were recorded. Then, each of the fresh polymer emulsionsamples was poured into a 250 ml glass bottle leaving no free space onthe top of the emulsion surface. Bottles were then sealed upappropriately with additional tape around the cover. The sealed bottleswere put in a 50° C. oven and aged for a period of time, then taken outand cooled down in room temperature. The pH value, solid content (top &bottom), and viscosity of aged polymer emulsion samples were measuredagain, and they were further observed for gel, grit or separation. Thetime aged in the oven was also recorded.

2. Bond Strength

Laminates prepared from adhesive compositions were cut into 15 mm widthstrips for T-peel test under 250 mm/min crosshead speed using a 5940Series Single Column Table Top System available from InstronCorporation. During the test, the tail of each strip was pulled slightlyby fingers to make sure the tail remained 90 degree to the peelingdirection. Three strips for each sample were tested and the averagevalue was calculated. Results were in the unit of N/15 mm. The higherthe value is, the better the bond strength is.

3. Heat Seal Strength

Laminates prepared from adhesive compositions were heat-sealed in aHSG-C Heat-Sealing Machine available from Brugger Company under 140° C.seal temperature and 300N pressure for 1 second, then cooled down andcut into 15 mm width strips for heat seal strength test under 250 mm/mincrosshead speed using a 5940 Series Single Column Table Top Systemavailable from Instron Corporation. Three strips for each sample weretested and the average value was calculated. Results were in the unit ofN/15 mm. The higher the value is, the better the heat seal strength is.

III. Examples

1. Preparation of Aqueous Polymer Emulsions

Inventive Examples 1

Monomer Emulsion Preparation: An emulsified monomer mixture was preparedby adding 435.0 g of DI water, 9.6 g of DS-4, 11.5 g of V3525, 854.5 gof BA, 36.0 g of AA and 548.0 g of VA slowly to the agitated solutionbefore polymerization.

Polymerization: A solution containing 0.9 g of sodium bicarbonate and730.0 g of DI water were placed in a 5-necked, 5-liter round bottomflask equipped with a thermocouple, a cooling condenser and an agitator,and heated to 74° C. under nitrogen. 0.01 g FeSO₄, 0.01 g EDTAtetrasodium salt, 3.2 g of APS and 28.7 g of perform seed in 51.0 g ofDI water were charged into the flask. When the temperature was at 74°C., monomer mixture and a co-feed solution of 3.2 g of APS solved in148.0 g DI water and 0.7 g of IAA solved in 148.0 g DI water were fed in210 minutes. The polymerization reaction temperature was maintained at73-75° C. Upon completion of the additions, the reaction mixture wascooled to 70° C. before gradual addition of a solution of 3.0 g t-BHP(70% active content) in 28.2 g DI water and 2.3 g SBS solved in 28.2 gDI water in 45 minutes with stirring. Upon completion of the feeds, thereaction was cooled to room temperature. 6.8 g Na₂CO₃ in 78.2 g DI waterwas then drop added in 30 minutes to adjust pH value to 6.0-8.0. Then,0.11 g of KATHON™ LX biocide was added with stirring in 30 minutes.Proper amount of DI water was added to adjust final solids to 42-45%.

Inventive Examples 2-8

Polymer emulsions were prepared by using the procedure outlined forInventive Example 1. The weights for the monomer emulsions are detailedin Table 1.

TABLE 1 α,β- ethylenically unsaturated carboxylic Monomer StabilizerVinyl ester Emulsion DI water Surfactant monomer acetate monomerInventive 435.0 g 9.6 g DS-4 11.5 g V3525; 548.0 g 854.5 g BA Example 136.0 g AA Inventive 435.0 g 9.6 DS-4 11.5 g V3535; 562.4 g 861.7 g BAExample 2 14.4 g AA Inventive 435.0 g 9.6 g DS-4; 11.5 g V3535; 656.1 g775.5 g BA Example 3 0.9 g 15-S-40 7.2 g AA Inventive 435.0 g 9.6 gDS-4; 11.5 g V3535; 562.4 g 861.7 g BA Example 4 0.45 g 15-S-40 14.4 gAA Inventive 435.0 g 9.6 g DS-4; 11.5 g V3535; 540.8 g 883.2 g BAExample 5 0.9 g 15-S-40 14.4 g AA Inventive 435.0 g 9.6 g DS-4; 11.5 gV3535; 540.8 g 883.2 g BA Example 6 0.9 g 15-S-40 14.4 g MAA Inventive435.0 g 9.6 g DS-4; 11.5 g V3535; 274.0 g 1148.9 g BA Example 7 0.9 g15-S-40 14.4 g AA Inventive 435.0 g 9.6 g DS-4; 11.5 g V3535; 1139.3 g 287.2 g BA Example 8 0.9 g 15-S-40 14.4 g AA

Comparative Example 1

Monomer Emulsion Preparation: An emulsified mixture was prepared byadding 435.0 g of DI water, 9.6 g of DS-4, 0.9 g of 15-S-40, 11.5 g ofV3535, 883.1 g of BA, 14.4 g of AA and 540.8 g of VA slowly to theagitated solution before polymerization.

Polymerization: A solution containing 0.9 g of sodium bicarbonate and587.3 g of DI water were placed in a 5-necked, 5 liter round bottomflask equipped with a thermocouple, a cooling condenser and an agitator,and heated to 74° C. under nitrogen. Charge 7.18 g HEC A dispersed in143.6 g hot water. Charge 0.01 g FeSO₄, 0.01 g EDTA tetrasodium salt,3.2 g of APS and 28.7 g of perform seed in 51.0 g of DI Water into thekettle. When the temperature was at 74° C., monomer emulsion and aco-feed solution of 3.2 g of APS solved in 148.0 g of DI water and 0.7 gof IAA solved in 148.0 g of DI water were fed in 210 minutes. Thepolymerization reaction temperature was maintained at 73-75° C. Uponcompletion of the additions the reaction mixture was cooled to 70° C.before gradual addition of solution of 3.0 g t-BHP (70% active content)in 28.2 g DI water and 2.3 g SBS solved in 28.2 g DI water in 45 minuteswith stirring. Upon completion of the feeds, the reaction was cooled toroom temperature. Add 6.8 g Na₂CO₃ in 78.2 g water solution drop addingin 30 minutes to adjust pH value to 6.0˜8.0. Then add 0.11 g of KATHON™LX biocide with stirring 30 minutes. Add proper amount of DI water toadjust final solids to 42-45%.

Comparative Example 2

Monomer Emulsion Preparation: An emulsified monomer mixture was preparedby adding 435.0 g of DI water, 9.6 g of DS-4, 0.9 g of 15-S-40, 11.5 gof V3535, 883.1 g of BA, 14.4 g of AA and 540.8 g of VA slowly to theagitated solution before polymerization.

Polymerization: A solution containing 0.9 g of sodium bicarbonate and605.0 g of DI water were placed in a 5-necked, 5 liter round bottomflask equipped with a thermocouple, a cooling condenser and an agitator,and heated to 74° C. under nitrogen. Charge 14.6 g PVOH A dispersed in125.0 g hot water. Charge 0.01 g FeSO₄, 0.01 g EDTA tetrasodium salt,3.2 g of APS and 28.7 g of perform seed in 51.0 g of DI Water into thekettle. When the temperature was at 74° C., monomer emulsion and aco-feed solution of 3.2 g of APS solved in 148.0 g of DI water and 0.7 gof IAA solved in 148.0 g of DI water were fed in 210 minutes. Thepolymerization reaction temperature was maintained at 73-75° C. Uponcompletion of the additions the reaction mixture was cooled to 70° C.before gradual addition of solution of 3.0 g t-BHP (70% active content)in 28.2 g DI water and 2.3 g SBS solved in 28.2 g DI in 45 minutes withstirring. Upon completion of the feeds, the reaction was cooled to roomtemperature. Add 6.8 g Na₂CO₃ in 78.2 g water solution drop adding in 30minutes to adjust pH value to 6.0˜8.0. Then add 0.11 g of KATHON™ LXbiocide with stirring 30 minutes. Add proper amount of DI water toadjust final solids to 42-45%.

Comparative Example 3

Monomer Emulsion Preparation: An emulsified monomer mixture was preparedby adding 435.0 g of DI water, 51.2 g of DS-4, 15.8 g of 15-S-40, 11.5 gof V3535, 789.8 g of BA, 14.4 g of AA and 634.5 g of VA slowly to theagitated solution before polymerization.

Polymerization: A solution containing 0.9 g of sodium bicarbonate and730.0 g of DI water were placed in a 5-necked, 5 liter round bottomflask equipped with a thermocouple, a cooling condenser and an agitator,and heated to 74° C. under nitrogen. Charge 0.01 g FeSO₄, 0.01 g EDTAtetrasodium salt, 3.2 g of APS and 28.7 g of perform seed in 51.0 g ofDI Water into the kettle. When the temperature was at 74° C., monomeremulsion and a co-feed solution of 3.2 g of APS solved in 148.0 g of DIwater and 0.7 g of IAA solved in 148.0 g of DI water were fed in 210minutes. The polymerization reaction temperature was maintained at73-75° C. Upon completion of the additions the reaction mixture wascooled to 70° C. before gradual addition of solution of 3.0 g t-BHP (70%active content) in 28.2 g DI water and 2.3 g SBS solved in 28.2 g DIwater in 45 minutes with stirring. Upon completion of the feeds, thereaction was cooled to room temperature. Add 6.8 g Na₂CO₃ in 78.2 gwater solution drop adding in 30 minutes to adjust pH value to 6.0˜8.0.Then add 0.11 g of KATHON™ LX biocide with stirring 30 minutes. Addproper amount of DI water to adjust final solids to 42-45%.

The weight percent of the surfactant, protective colloid, stabilizermonomer, vinyl acetate and α,β-ethylenically unsaturated carboxylicester monomer in Inventive Examples 1 to 8 and Comparative Examples 1 to3 are detailed in Table 2.

TABLE 2 α, β- ethylenically unsaturated Aqueous carboxylic PolymerProtective Stabilizer ester Emulsion Surfactant* colloid* monomer**Vinyl acetate** monomer** Inventive 0.15% DS-4 0 0.2% V3525;   38% 59.3%BA Example 1 2.5% AA Inventive 0.15% DS-4 0 0.2% V3525;   39% 59.8% BAExample 2 1% AA Inventive 0.15% DS-4; 0 0.2% V3525; 45.5% 53.8% BAExample 3 0.04% S-15-40 0.5% AA Inventive 0.15% DS-4; 0 0.2% V3525;  39% 59.8% BA Example 4 0.02% S-15-40 1% AA Inventive 0.15% DS-4; 00.2% V3525; 37.5% 61.3% BA Example 5 0.04% S-15-40 1% AA Inventive 0.15%DS-4; 0 0.2% V3525; 37.5% 61.3% BA Example 6 0.04% S-15-40 1% MAAInventive 0.15% DS-4; 0 0.2% V3525;   19% 79.8% BA Example 7 0.04%S-15-40 1% AA Inventive 0.15% DS-4; 0 0.2% V3525; 78.9% 19.9% BA Example8 0.04% S-15-40 1% AA Comparative 0.15% DS-4; 0.5% 0.2% V3525; 37.5%61.3% BA Example 1 0.04% S-15-40 HEC A 1% AA Comparative 0.15% DS-4;  1% 0.2% V3525; 37.5% 61.3% BA Example 2 0.04% S-15-40 PVOH A 1% AAComparative 0.80% DS-4; 0 0.2% V3525;   44% 54.8% BA Example 3 0.70%S-15-40 1% AA *by dry weight, based on total dry weight of the polymer**as polymerized units, by dry weight, based on total dry weight of thepolymer

2. Preparation of Aqueous Adhesive Compositions

The above aqueous polymer emulsions are used as aqueous adhesivecompositions without further formulations.

3. Preparation for Laminates

BOPP and VMCPP films were used without any pre-treatment. The adhesivewas coated on BOPP, dried and combined with VMCPP films to obtainBOPP/adhesive/VMCPP film composite with adhesive coating weight of 1.8g/m² on dry weight basis. Then the combined BOPP/adhesive/VMCPP filmcomposite was curing on 50° C. for 1 day.

IV. Application Performance Test Results

As Table 3 illustrates, all aqueous polymer emulsions of InventiveExamples 1 to 8 meet performance requirement, and exhibit good emulsionstorage stability (greater than 1 month) and low viscosity (less than100 cps). Both aqueous polymer emulsions of Comparative Example 1 andComparative Example 2, which use HEC or PVOH respectively as protectivecolloid, exhibit high viscosity (greater than 300 cps) and poor emulsionstorage stability (grit greater than 1%). Although Comparative Example 4(Rovace™ Binder 662) exhibits good emulsion storage stability, theviscosity (greater than 300 cps) is higher than the desired performancerequirement of less than 100 cps, due to the high surfactant level andadded protective colloid.

TABLE 3 Aqueous Emulsion Polymer Protective Storage Viscosity EmulsionSurfactant* colloid* Stability (cps) Tg (° C.)** Inventive 0.15% DS-40 >1 month 15-20 −27° C. Example 1 (grit < 0.2%) Inventive 0.15% DS-40 >3 months 15-20 −28° C. Example 2 (grit < 0.2%) Inventive 0.15% DS-4;0 >5 months 15-20 −23° C. Example 3 0.04% S-15-40 (grit < 0.2%)Inventive 0.15% DS-4; 0 >3 months 15-20 −28° C. Example 4 0.02% S-15-40(grit < 0.2%) Inventive 0.15% DS-4; 0 >5 months 15-20 −29° C. Example 50.04% S-15-40 (grit < 0.2%) Inventive 0.15% DS-4; 0 >5 months 15-20−28.7° C.   Example 6 0.04% S-15-40 (grit < 0.2%) Inventive 0.15% DS-4;0 >3 months 15-20 −43° C. Example 7 0.04% S-15-40 (grit < 0.2%)Inventive 0.15% DS-4; 0 >3 months 15-20    8° C. Example 8 0.04% S-15-40(grit < 0.2%) Comparative 0.15% DS-4; 0.5% HEC A grit > 1% >300 −29° C.Example 1 0.04% S-15-40 Comparative 0.15% DS-4; 1% PHOV A grit > 1% >300−29° C. Example 2 0.04% S-15-40 Comparative N/A N/A >3 months >300 N/AExample 4: (grit < 0.2%) Rovace ™ 662 *By dry weight, based on total dryweight of the polymer **Tgs herein are calculated using the Fox Equation(T. G. Fox, Bull. Am. Physics Soc., Volume 1, Issue 3, page 123 (1956)).

As Table 4 illustrates, laminates prepared from the aqueous adhesivecomposition comprising aqueous polymer emulsions of Inventive Examples 3to 5 exhibit good bond strength (greater than 1.0N/15 nm) and heat sealstrength (greater than 10N/15 nm) adhesive performances. Especially,Inventive Example 5 shows optimized performance comparable toComparative Example 5 (Robond™ Binder L-70D prepared fromstyrene-acrylic emulsion) which is used as a benchmark for performancegoals. Although aqueous polymer emulsion of Comparative Example 3exhibits good stability and low viscosity, the bond strength (less than0.5N/nm) of the laminate prepared from the aqueous adhesive compositioncomprising aqueous polymer emulsion of Comparative Example 3 is muchlower than Inventive Example 3 to 5 due to the high surfactant level.

TABLE 4 Bond Heat Seal Protective Strength Strength LaminatesSurfactant* colloid* (N/15 nm) (N/15 nm) Inventive 0.15% DS-4; 0 1.114.6 Example 3 0.04% S-15-40 Inventive 0.15% DS-4; 0 1.27 15 Example 40.02% S-15-40 Inventive 0.15% DS-4; 0 1.5 15.6 Example 5 0.04% S-15-40Comparative 0.80% DS-4; 0 <0.5 N/A Example 3 0.70% S-15-40 ComparativeN/A N/A 1.54 15 Example 5: ROBOND ™ L-70D

What is claimed is:
 1. An aqueous polymer emulsion comprising: i) aspolymerized units, from 20% to 80% by dry weight, based on total dryweight of the polymer, of vinyl acetate; ii) as polymerized units, from20% to 80% by dry weight, based on total dry weight of the polymer, ofan α,β-ethylenically unsaturated carboxylic ester monomer; iii) aspolymerized units, from 0.1% to 5% by dry weight, based on total dryweight of the polymer, of a stabilizer monomer selected from the groupconsisting of sodium styrene sulfonate, sodium vinyl sulfonate,2-acrylamido-2-methylpropanesulfonic acid, acrylamide, acrylic acid,methacrylic acid, itaconic acid, and any combinations thereof; iv) from0.05% to 1% by dry weight, based on total dry weight of the polymer, ofa surfactant, where said aqueous polymer emulsion further comprises avinyl ester monomer other than vinyl acetate, where said aqueous polymeremulsion has a viscosity of less than 100 cps.
 2. The aqueous polymeremulsion according to claim 1, wherein said aqueous polymer emulsion hasa viscosity of less than 30 cps.
 3. The aqueous polymer emulsionaccording to claim 1, wherein said aqueous polymer emulsion comprising,from 0.05% to 0.5% by dry weight, based on total dry weight of thepolymer, of a surfactant.
 4. The aqueous polymer emulsion according toclaim 1, wherein said surfactant is a combination of an anionicsurfactant and a non-ionic surfactant with a mole ratio of the ionicsurfactant to that of the non-ionic surfactant being 0.5-20.
 5. Theaqueous polymer emulsion according to claim 1, wherein said aqueouspolymer emulsion does not comprise a protective colloid.
 6. The aqueouspolymer emulsion according to claim 1, wherein said aqueous polymeremulsion has a glass transition temperature of 8° C. to −43° C.
 7. Theaqueous polymer emulsion according to claim 1, wherein said aqueouspolymer emulsion has a glass transition temperature of −23° C. to −30°C.
 8. The aqueous polymer emulsion according to claim 1, wherein saidaqueous polymer emulsion has a particle size from 150 nm to 500 nm. 9.The aqueous polymer emulsion according to claim 1, wherein saidα,β-ethylenically unsaturated carboxylic ester monomer is (meth)acrylicester monomer.
 10. An aqueous adhesive composition comprising theaqueous polymer emulsion according to claim 1.